1. Field of the Invention
The invention relates to thickener compositions and to their use for thickening water-dilutable systems, such as inks, paints and binders, which can be mixed homogeneously or diluted with water.
2. Description of the Prior Art
Thickeners based on polyurethanes and their use for thickening water-dilutable systems are described in numerous publications (e.g. DE-A 1,444,243, 3,630,319 and 4,310,702; EP-A 0,307,775 and 495,373; and U.S. Pat. Nos. 4,079,028, 4,155,892, 4,499,233 and 5,023,309).
A common feature of these thickeners is the simultaneous presence of linear or branched polymers which contain hydrophilic segments (e.g., polyether chains containing at least 5 alkylene oxide units, preferably ethylene oxide units), hydrophobic segments (e.g., hydrocarbon segments containing at least 6 carbon atoms) and urethane groups. These prior art thickeners are suitable for use as component A) according to the invention.
These polyurethane thickeners are suitable for adjusting or modifying the rheological properties of aqueous compositions, e.g., industrial paints, water-based plasters and paints, printing and textile printing inks, pigment printing inks, pharmaceutical and cosmetic aqueous compositions such as creams, plant protection formulations and filler dispersions.
In addition to these polyurethane thickeners, which are also known as "active substances," the prior art thickener compositions may also contain nonionic emulsifiers, additives and water. A disadvantage of these compositions is that in the form of aqueous solutions, they have a high viscosity which makes it difficult to incorporate them into water-dilutable systems.
A number of attempts have been described to reduce the viscosity of thickeners. For example, the molecular weight can be reduced, but this impairs the rheological properties. Various emulsifiers and other additives with emulsifying properties have also been suggested. However, this also impaired the rheological properties.
Another known method for lowering the viscosity is the addition of water-miscible solvents, e.g. monohydric or polyhydric alcohols. However, this usually leads to a deterioration of environmental compatibility and in some cases a deterioration of application properties of the aqueous preparations, such as brushing characteristics or stability.
An object of the present invention is to provide new polyurethane-based thickener compositions for aqueous systems which, in the form of their aqueous solutions, emulsions or dispersions, have a reduced viscosity, but also provide improved rheological properties when compared to prior art compositions.
Surprisingly, this object may be achieved in accordance with the present invention by the addition of certain short-chain esters, which are described in more detail below, as additional additives to the polyurethane-based thickeners.